Plasma discharges have been employed to provide accelerated charged particles for many years. To date, two main operating modes of such plasma discharges have been identified. In the first mode, sometimes referred to as the snowplow mode, a plasma gun is allowed to fill with gas before high electric voltage is switched to the electrodes. When the voltage is applied, the gas breaks down, typically at the breech of the plasma gun, and forms a narrow current sheet that is pushed downstream by the j×B force.
The second mode is sometimes referred to as the plasma deflagration mode, and can be accessed by reversing the order of gas injection and voltage switching relative to the snowplow mode. In the deflagration mode, breakdown occurs at the gas front, and the discharge region travels upstream to process new gas entering the electrode gap. The deflagration discharge region can be made stationary by establishing a downstream gas flow. In either case, the processed gas is accelerated downstream without being significantly inhibited through collisions with downstream gas. Since the processed gas in the snowplow mode experiences collisions, the deflagration mode has the potential to provide higher output particle velocity than the snowplow mode.
The difference between the snowplow mode and a plasma deflagration is analogous to the difference between an explosive shock front (detonation) and a flame (deflagration) in combustion theory. A detonation deposits its available energy predominantly into heating and compression whereas a deflagration deposits a higher fraction into directed kinetic energy. As a result, a plasma deflagration can produce directed gas speeds that are several times higher than in the snowplow mode (detonation) case. Further information relating to the plasma deflagration mode can be found in an article by Cheng entitled “Plasma deflagration and the properties of a coaxial plasma deflagration gun” (Nuclear Fusion v 10 1970, pp 305-317), and hereby incorporated by reference in its entirety.
Although the plasma deflagration mode can provide higher particle velocity than the snowplow mode, it remains desirable to further increase particle velocity.